Then just swap pins 2 and 3. But why not run the signal through one of the transmitters, and put a=20 diode in series with the output? Cathode to transmitter output, anode=20 to resistor to ground, take signal out from anode. Kerry alan smith wrote: > what I need is when the input is +5 and need it to be -5 out, and when it= s low...the output to be low...so basically inverting it. > > > > ----- Original Message ----- > From: Kerry Wentworth > To: Microcontroller discussion list - Public. > Cc:=20 > Sent: Monday, October 31, 2011 9:19 AM > Subject: Re: [EE] -5V to 0V swing from a +5 input (again) > > I don't remember the details of what you are looking for, but for=20 > argument's sake, let's assume you want +5V in to give 0V out, and 0V in=20 > to give -5V out. > > You could use an LM311 voltage comparator. Use your +8V and -8V (or +-=20 > 5V) to power it. Tie the output pin (7) to ground and tie the "ground"=20 > pin to a pulldown resistor to -5V. Tie the + input (2) to a voltage=20 > between 0V and 5V (say 2.5V). Apply the signal to the - input (3). > > Kerry > > > alan smith wrote: > =20 >> hello...this goes back to a question I asked a few weeks ago. Basically= it was asking about generating a -5V signal from a +5V input. >> >> So I settled on a ADM222, old style RS232 driver and sure enough I can g= et the -8V drive. But what I need is -5V so thinking....on the charge pump= -V pin, putting a zener to clamp the voltage to -5V....or....feeding that = -V pin with a regulated -5V, wondering if that might work. >> >> However the other problem is, when the input is positive, the output goe= s positive, and I need that to be at the reference 0V level. I tried to us= e a pull down to ground on the +V charge pump, but that just pulled it from= +8V to +5V. I'm not an analog oriented person so...wondering if there is = some sort of opamp based design that can only allow the negative swing to g= o thru, and if its ever positive, keep it at the ground reference. What ha= ppens if you ground the positive rail on an opamp and just provide negative= power? =20 >> >> >> =20 >> =20 > > =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .